Chelsea manager Jose Mourinho has admitted that he is concerned by star striker Diego Costa's ongoing hamstring injuries.

The 26-year-old missed most of the Blues' run-in en route to Premier League glory last season before appearing in their final two games of the campaign.

Having missed Sunday's Community Shield defeat to Arsenal and last night's 1-0 reverse to Fiorentina, speculation has mounted that he will also sit out their curtain-raiser with Swansea on Saturday.

"Costa is not ready. It is not a good feeling for him, it is not a good feeling for me," Mourinho told reporters.

"I have to be honest and say that it is a bit of a concern. A player that didn't finish the season and [then] doesn't start the season obviously doesn't make me happy.

"The scans show there is no injury so next day he trains, but the next day he is not comfortable. Then, 24 hours before the [Community Shield], we don't know if he plays or doesn't play."

Costa netted 20 times in 26 Premier League appearances last season.